Medical catheters are used for innumerable minimally invasive medical procedures. Catheters, specifically, injection catheters, may be used, for example, for delivery of therapeutic drug doses to target tissue and/or for delivery of medical devices such as lumen-reinforcing or drug-eluting stents. Likewise, catheters may be used to guide medical instruments to a target site to perform a surgical procedure, such as tissue rescission, ablation of obstructive deposits or myocardial revascularization.
Currently, injection-catheter-based systems include catheters with and without sensors. Injection-catheters without sensors have an opening at the distal end of the catheter to permit a needle or a medical device to pass through the opening and into a target tissue site in the patient. Injection-catheters that are equipped with sensors (for example, electrodes) have a sensor tip at the distal end of the catheter with an opening to permit a needle or a medical device to pass through the opening and into target tissue in the patient. The sensor systems usually have one or more additional return sensors implemented as bands circumferentially around the catheter. In some systems, tissue contact is determined by measuring the impedance between the tip sensor when it is in contact with tissue and a return sensor that is not in contact with the tissue but is only in contact with a fluid, for example, blood, that is surrounding the tissue. However, this determination is based on known, that is, pre-determined, impedance values when the electrode is in contact with tissue and when only in contact with body fluids (for example, blood).
Likewise, needles used with injection-catheters currently work by positioning the device over tissue at the injection site, pushing the needle out of the catheter and into the tissue, delivering a therapeutic agent into the tissue, and retracting the needle. However, this usually results in the loss of some of the therapeutic agent from the tissue when the needle is withdrawn, which can not only diminish the effectiveness of the injected therapeutic agent, but also cause adverse side-effects due to the lost therapeutic agent travelling to undesirable locations within the patient. The local delivery of therapeutic agents to heart-wall and coronary arteries has shown promise in treating heart disease. These agents include gene therapies, drugs, proteins, extracellular matrices, and cells. Localized delivery is important due to potential adverse effects associated with systemic delivery of the therapy and the therapeutic benefit of a concentrated dose delivered to the affected site. Unfortunately, current injection-catheters do not enable the optimal targeted delivery of therapeutic agents to provide the most effective treatment regimen, since the tissue in which the therapeutic agent is delivered does not always retain all of the injected therapeutic.